1. Field of the Invention
The present invention relates to a reciprocating positive displacement pump particularly suitable for the pumping of oenological liquids such as wines, musts, distillates, vinegars and the like, of alimentary oils and of other alimentary liquids and/or beverages such as fruit juices and pulps, sugary juices, etc.
2. Prior Art
As is know, in order to pump oenological liquids and alimentary liquids in general by means of reciprocating piston type positive displacement pumps it is necessary that the liquids undergo the least possible agitation during the pumping operations in order to preserve their organoleptic characteristics, which would in fact be altered and/or comprised by the agitation and the forming of emulsions with air which always occur during turbulent motion.
In order to reduce the conditions of turbulence of oenological and alimentary liquids during their decanting from one container to another, the food industry employs single- or two-cylinder positive-displacement piston pumps, the actuation stem of which is reciprocatingly actuated by a connecting-rod/crank system. In particular, the positive displacement pumps used are normally of the single- or two-cylinder kind with distribution provided by ball valves made of rubber with metallic central cores. In these cases the length of the stroke of the piston is equal to the diameter of the circle traced by the small end of the connecting rod.
The reciprocating actuation system with connecting rod and crank has in practice various disadvantages and operative limitations.
The actuation system in fact provides a liquid flow which is pulsating rather than constant due to the fact that the speed of the piston (and therefore of the liquid) varies for each stroke of the piston from a zero value when the piston is at one end of the cylinder to a maximum value at mid-stroke and then back to the zero value at the end of the stroke. The change in the flow-rate of the liquid and therefore in the speed thereof entails considerable turbulence of the liquid which results in high stresses on the delivery pipes and a water hammer effect, as well as possible wear and/or breakage of the pipes. The disadvantage is worsened by the fact that in oenological plants the pipes are normally made of flexible material and are generally not coupled to fixed supports. Assuming constant piston diameter and speed, the liquid flow-rate is dependent on the maximum length of the piston's stroke which, in practice, is defined by the diameter of the circle defined by the connecting rod's small end, which depends on the diameter of the flywheel used to actuate the piston's system.
Since it is not convenient to use pistons and flywheels having diameters greater than certain limits due to pump cost and ease-of-handling reasons, in practice the maximum obtainable flow-rates are relatively modest.